When a substance such as human tissue is subjected to a uniform magnetic field (polarizing field B0), the individual magnetic moments of the excited nuclei in the tissue attempt to align with this polarizing field. If the substance, or tissue, is subjected to a magnetic field (excitation field B1) that is in the x-y plane and that is near the Larmor frequency, the net aligned moment, Mz, may be rotated, or “tipped”, into the x-y plane to produce a net transverse magnetic moment Mt. A signal is emitted by the excited nuclei or “spins”, after the excitation signal B1 is terminated as the nuclei precess about B0 at their characteristic Larmor frequency. This signal may be received and processed to form an image.
When utilizing these magnetic resonance “MR” signals to produce images, magnetic field gradients (Gx, Gy and Gz) are employed. Typically, the region to be imaged is scanned by a sequence of measurement cycles in which these gradients vary according to the particular localization method being used. The resulting set of received MR signals are digitized and processed to reconstruct the image using one of many well known reconstruction techniques.
The measurement cycle used to acquire each MR signal is performed under the direction of a pulse sequence produced by a pulse sequencer. The MR signals acquired with an MRI system are signal samples of the subject of the examination in Fourier space, or what is often referred to in the art as “k-space”. Each MR measurement cycle, or pulse sequence, typically samples a portion of k-space along a sampling trajectory characteristic of that pulse sequence.
MRI systems constructed for acquiring MR signals typically include a superconducting magnet provided in a toroidal housing including a bore that is dimensioned to receive a patient to be imaged. The magnet produces the polarizing field B0 axially through the bore, and whole body radio frequency and gradient coils typically surround the bore. In operation, a patient is transported to the bore on a wheeled or otherwise movable patient transport. A patient support is provided on the transport, and this support can be selectively inserted into the bore for imaging, and subsequently retracted.
When performing scans of a selected anatomy of the patient, such as the breast, head or heart, local RF coils configured for the selected anatomy are commonly positioned in the bore with the patient. To provide flexibility for image acquisition, it is desirable to allow medical personnel to select specific RF coil configurations, and to selectively position these RF coils adjacent the anatomy of interest where needed, to allow for the acquisition of a variety of different views. When using a variety of coils and coil connectors however, it is important for the MRI system to be able to identify the RF coil configurations used, as well as their location, prior to a scan. Identification and verification of the coil, however, is complicated by the electromagnetic interference produced by the MRI system itself. The present invention addresses these issues.